clutch confusion - li to gp?

Hi, Sunday afternoon woes..pleased with myself in changing from an L125 gearbox to a GP200 one ..but went to put clutch back in and I have a spigot in the middle of clutch pressure plate housing,,,checked old gear cluster tree and see it had a hole in receive the spigot, gp one doesn't.
so looked on line and i can see the clutch pressure plate housings are different differ but also looks like i need to change side casing? anyone confirm if this is true please and if not options and work arounds.
text from cooter centre web page says: ''With the change from the Li-SX range to the dl/GP models the clutch was much improved. The dl/GP style clutch is the right choice for all heavily tuned Lambrettas. For using of this clutch pressure plate you have to change the side casing cover as well.''
Thanks
so looked on line and i can see the clutch pressure plate housings are different differ but also looks like i need to change side casing? anyone confirm if this is true please and if not options and work arounds.
text from cooter centre web page says: ''With the change from the Li-SX range to the dl/GP models the clutch was much improved. The dl/GP style clutch is the right choice for all heavily tuned Lambrettas. For using of this clutch pressure plate you have to change the side casing cover as well.''
Thanks